Technical Field
The present disclosure generally relates to the field of passive wireless transponders, more specifically to communication between passive wireless transponders in the presence of an externally applied carrier wave.
Description of the Related Art
Passive wireless transponders such as radio frequency identification tags typically include an antenna, a control circuit or controller, and a limited quantity of nontransitory storage. Typically, each passive wireless transponder includes data indicative of a unique identifier hardwired or stored in the nontransitory storage (e.g., nonvolatile memory). Additionally, logic or machine executable instruction sets executable by the control circuit or controller may be optionally hardwired or stored in the nontransitory storage. Passive wireless transponders receive energy when illuminated or interrogated by a carrier wave within a particular frequency range. When energized, passive wireless transducers may backscatter waves which may or may not carry data. Additionally, the passive wireless transponders may execute one or more sets of machine executable instructions when energized. Such machine executable instructions permit passive wireless transponders to perform additional functions such as transmitting stored data, writing to nontransitory storage or interacting with the ambient environment.
Typically, a reader or interrogator transmits a carrier wave to energize the passive wireless transponders. The reader and interrogator also typically receives backscatter signals from the energize passive wireless transponders. The reader may decode or interpret information encoded or imposed on the backscatter signals. Sometimes one or more readers or interrogators are communicably coupled to a host or backend processor-based system. The interrogator extracts the data carried by the backscatter waves produced by each passive wireless device within range of the interrogator. Using the extracted data, the interrogator is able to perform various functions including information lookup (e.g., determining the type and price of an item to which the passive wireless transponder is attached) and position determination (e.g., indicating an approximate direction and distance to a particular passive wireless transponder).